Thermoformed vacuumed containers are well known in the art of packaging rigid products such as hot dogs and cheeses. The automatic packaging machines in commercial use typically assemble such containers from two continuous webs of plastic material that are supplied as rollstock. In such machines, a lower web of rigid material is first thermoformed into a series of cup-shaped lower containers, each cup having a peripheral flange around its mouth. Thereafter, a rigid product is placed within each cup before they are indexed to an evacuation/sealing chamber. Inside the chamber, the cups are evacuated, followed by heat sealing an upper web to the peripheral flange surrounding each cup. The series of heat-sealed cups are then removed from the evacuation/sealing chamber for further processing, which typically includes cutting or stamping the series of cups into individual packages ready to be placed inside shipping cartons.
In order to achieve material cost savings, some thermoform/vacuum processes utilize webs of flexible material in packaging rigid products. When such flexible film packages are evacuated, sealed, and removed from the sealing/evacuation chamber, the pressure differential between inside and outside the package causes the flexible film to shrivel into close contacting relation with the product therein. Since the product is rigid and has a relatively constant shape, the package's final shape is the same as the product itself, which typically is an easy to handle shape such as square or rectangular. Therefore, using flexible films in vacuum packing rigid products is a relatively simple matter.
Special care must be taken when granular or flowable products are vacuum packed within thermoformed containers. As pointed out in U.S. Pat. No. 4,424,659, which issued to Perigo et al. and is hereby incorporated herein by reference, it is necessary to leave a "headspace" between the surface level of the flowable product and the heat-sealing surface of the cup's peripheral flange in order to avoid contaminating this surface or otherwise causing interference between the upper web and the sealing surface during the heat-sealing operation. The headspace is particularly necessary when vacuum packaging a light granular product such as ground coffee because turbulence created during the evacuation step can draw granules out of the cup and deposit them on the cup's flange.
In order to achieve substantial material cost savings over the shape retaining, thermoformed containers of the type generally disclosed in Perigo, the present invention utilizes thin, non-shape retaining or flexible films in vacuum packing granular products. However, it has been found that using flexible film material for the lower cup presents several troublesome problems. Specifically, when such a flexible film container filled with a granular product is removed from the sealing/evacuation chamber, atmospheric pressure outside the container shrivels the lower cup and pushes the product up into the headspace. Since the product does not have a shape of its own, the resultant package assumes a random shape that is very difficult to handle during subsequent processing operations. In addition, such a shrivelled, randomly-shaped package has an outer appearance that looks something like a prune. It has been found that most consumers find such a package unattractive. Finally, the randomly-shaped and shrivelled film often includes sharp ridges and valleys that are prone to scuffing and abrasion during subsequent handling operations. If the scuffing or abrasions are excessive the film might develop small holes which would allow oxygen to enter the package and product to escape.
In light of the above, a principal object of the present invention is to achieve significant material cost savings in vacuum packaging a granular produce in a thermoformed container by making the container's lower cup from flexible, non-shape retaining films.
Another principal object of the present invention is to provide a thermoformed, flexible film, vacuumed container having a granular product therein with a predetermined, constant shape.
Another principal object of the present invention is to provide a thermoformed, flexible film, vacuumed container having a granular product therein with an aesthetically pleasing appearance.
Another object of the present invention is to provide a thermoformed, flexible film, vacuumed container that exhibits a reduced amount of wrinkling and a corresponding higher degree of abrasion resistance.
Another object of the present invention is to provide a thermoformed, flexible film, vacuumed container that is solid, relatively easy to open, and exhibits good oxygen and moisture barrier properties.
A further object of the present invention is to provide an economical manufacturing method of making reshaped, vacuumed, flexible film packages for granular products.
Another object of the present invention is to provide efficient apparatus for making reshaped, vacuumed, flexible film packages for granular product.